The present invention relates to nanotweezers that grip and release substances that have a size on the order of nanometers (hereafter referred to as xe2x80x9cnano-substancesxe2x80x9d) and further relates to a nanomanipulator device which can assemble nano-size parts and nano-molecular devices, etc. by moving and stacking nano-substances.
Technological development in recent years has been increasingly oriented toward the ultra-small region. For example, there has been a demand for the development of revolutionary manufacturing techniques in the nano-region, as seen in the creation of new materials and nano-size parts in the optical and electronic information fields, and in the creation of new bio-related functional substances by the integration of cells and proteins.
In order to move and stack nano-substances in this manner, it is necessary to develop nanotweezers that can grip and release nano-substances. A first prototype of such nanotweezers has been announced by Philip Kim and Charles M. Lieber in the Journal of Science published on Dec. 10, 1999. FIGS. 16 through 18 are diagrams of the manufacturing process of these nanotweezers.
FIG. 16 is a side view of the tip end of a glass tube that has been worked so that a taper is formed. The diameter of this tip end is approximately 100 nm, while the diameter of the rear end of the tube not shown is 1 mm. FIG. 17 is a complete diagram of a set of nanotweezers. Two metal electrode films 84a and 84b are formed on the circumferential surface of the above-described glass tube 80 with an insulating section 82 interposed. Carbon nanotubes 86a and 86b are respectively fastened to these metal electrode films so that the carbon nanotubes protruded, thus forming a set of nanotweezers 88.
FIG. 18 is a schematic diagram showing the application of a voltage to the nanotweezers. Lead wires 92a and 92b are led out from contact points 90a and 90b on the metal electrode films 84a and 84b and are connected to both ends of a direct-current power supply 94. When the voltage of this direct-current power supply 94 is applied, the carbon nanotube 86a is charged to a positive polarity, while the carbon nanotube 86b is charged to a negative polarity. As a result of the electrostatic attractive force of these positive and negative charges, the tip ends of the carbon nanotubes 86a and 86b close inward, so that a nano-substance 96 can be gripped between these tip ends.
If the voltage is increased, the carbon nanotubes close even further, so that a smaller nano-substance can be gripped. If the voltage is reduced to zero, the electrostatic attractive force is eliminated, so that the carbon nanotubes 86a and 86b are caused to return to the state shown in FIG. 17 by the elastic recovery force of the carbon nanotubes 86a and 86b, thus releasing the nano-substance 96. Thus, the nanotweezers are advantageous in that the opening-and-closing control of the nanotweezers 88 can be accomplished merely by controlling the magnitude of a voltage as described above, so that the nanotweezers represent a break-through in terms of nanotweezers.
However, the nanotweezers 88 have the drawbacks. More specifically, the first drawback is that since the tip end of the glass tube 80 is finely worked to 100 nm in a tapered form, thus the nanotweezers 88 are weak and brittle in terms of strength.
The second drawback is that the metal electrode films 84a and 84b are formed along the entire length of the glass tube 80; and the contact points 90a and 90b are disposed on the large-diameter rear portion of the glass tube and are connected to the power supply 94 via the lead wires 92a and 92b. In other words, the lead wires have a considerable thickness; as a result, the electrical contact points must be disposed on the rear end portion of the glass tube, which has an expanded diameter. This results in the difficulty of forming the metal electrode films along the entire length of the glass tube and in poor efficiency.
The third drawback arises from the fact that the nanotweezers are electrostatic nanotweezers. More specifically, in the case of electrostatic nanotweezers, positive and negative electrical charges are accumulated in the carbon nanotube, and the opening and closing actions of the carbon nanotubes are controlled by the electrostatic attractive force of these electrical charges. In cases where the nano-substance 96 is an electrical insulator or a semiconductor, such an electrostatic attractive force can be utilized. However, in cases where the nano-substance is a conductor, the ends of the carbon nanotubes are electrically short-circuited, so that such an electrostatic attractive force ceases to operate. Furthermore, there is also a danger that the nano-substance will be electrically destroyed in the case of short-circuiting. Accordingly, such nanotweezers suffer from such weak points that the use of the nanotweezers is limited to semiconductor nano-substance and insulating nano-substances, and constant care must be taken during use.
The fourth drawback is that the nanotweezers are constructed from two carbon nanotubes. In other words, molecules have various shapes, and there are nano-substances that cannot be securely gripped by two nanotubes. For example, flattened nano-substances can be gripped by the two carbon nanotubes 86a and 86b. However, in cases where spherical nano-substances or rod-form nano-substances are gripped, the gripping thereon is unstable, and there is a danger that the nano-substance will fall out of the nanotweezers.
Accordingly, a first object of the present invention is to provide nanotweezers that have a high strength and are relatively easy to work.
Furthermore, a second object of the present invention is to provide nanotweezers that can grip conductive nano-substances, semiconductor nano-substances and insulating nano-substances without using an electrostatic system.
Furthermore, a third object of the present invention is to provide nanotweezers which can securely grip and transfer nano-substances of various shapes including spherical nano-substances, rod-form nano-substances, etc.
Furthermore, a nanomanipulator device which can assemble nano-structures is realized way of using the nanotweezers.
The first embodiment of the present invention is for nanotweezers which are characterized in that the nanotweezers comprise a plurality of nanotubes whose base end portions are fastened to a holder so that the nanotubes protrude from the holder, a coating film which covers the surfaces of the nanotubes with an insulating coating, and lead wires which are connected to two nanotubes among such nanotubes; wherein the tip ends of the two nanotubes are freely opened and closed by means of an electrostatic attractive force created by applying a voltage across the lead wires.
The second embodiment of the present invention is for nanotweezers which are characterized in that the nanotweezers comprise a pyramid portion which is installed on a cantilever so that the pyramid portion protrudes from the cantilever, a plurality of nanotubes whose base end portions are fastened to this pyramid portion so as to protrude from the pyramid portion and lead wires which are connected to two nanotubes among the nanotubes; wherein the tip ends of the two nanotubes can be freely opened and closed by means of an electrostatic attractive force created by applying a voltage across the lead wires.
The third embodiment of the present invention is for nanotweezers which are characterized in that the nanotweezers comprise a plurality of nanotubes whose base end portions are fastened to a holder so that the nanotubes protrude from the holder, and a piezo-electric film which is formed on the surface of at least one nanotube among these nanotubes; wherein the tip ends of the nanotubes are freely opened and closed by applying a voltage to the piezo-electric film so that the piezo-electric film is caused to expand and contract.
The fourth embodiment of the present invention is for the nanotweezers claimed in the third embodiment, wherein the holder is the pyramid portion of a cantilever.
The fifth embodiment of the present invention is for nanotweezers which are characterized in that the nanotweezers comprise a plurality of deformable pyramid pieces which form pyramid portion of a cantilever, nanotubes which are fastened to the tip ends of the pyramid pieces, and a piezo-electric film which is formed on the side surface of at least one pyramid piece; wherein the tip ends of the nanotubes are opened and closed by applying a voltage to the piezo-electric film so that the piezo-electric film is caused to expand and contract with the pyramid pieces being freely flexible.
The sixth embodiment of the present invention is for electrostatic nanotweezers which are characterized in that the electrostatic nanotweezers comprise three or more conductive nanotubes whose base end portions are fastened to a holder so as to protrude from the holder, and lead electrodes which are respectively connected to three or more conductive nanotubes among the nanotubes; wherein the conductive nanotubes are freely opened and closed by means of an electrostatic attractive force created by applying a voltage across the lead electrodes.
The seventh embodiment of the present invention is for electrostatic nanotweezers which are characterized in that the nanotweezers comprise a protruding portion which is disposed on a cantilever so that that the protruding portion protrudes from the cantilever, three or more conductive nanotubes whose base end portions are fastened to the protruding portion so as to protrude from the protruding portion, and lead electrodes which are respectively connected to each one of three or more of the nanotubes among the conductive nanotubes; wherein the tip ends of the conductive nanotubes are freely opened and closed by an electrostatic attractive force created by applying a voltage across the lead electrodes.
The eighth embodiment of the present invention is for a nanomanipulator which is characterized in that the nanomanipulator is comprised of the nanotweezers claimed in the first through seventh embodiments, and a three-dimensional driving mechanism which moves and controls the nanotweezers in X, Y and Z directions with respect to a sample; and nano-substances are transferred to the sample by the nanotweezers.
The ninth embodiment of the present invention is the nanomanipulator device claimed in the eight embodiment, wherein at least one of the nanotubes that form the nanotweezers is used as a probe needle of a scanning probe microscope.
The term xe2x80x9cpyramid portionxe2x80x9d is used in the same meaning as the term xe2x80x9cprotruding portionxe2x80x9d of the cantilever.
As a result of diligent research conducted for the purpose of developing nanotweezers possessing durability, the inventors of the present application succeeded in improving electrostatic attraction type nanotweezers utilizing the above-described nanotubes and further succeeded in developing high-performance piezo-electric film type nanotweezers.
First, a weak point of conventional electrostatic attraction type nanotweezers is that the nanotubes are electrically short-circuited in cases where the nano-substance that is being gripped is a conductive substance, so that the tweezers function is lost and there is a danger of breakage. In order to alleviate this drawback, nanotweezers are hereby proposed in which a coating film consisting of an insulating substance is formed on the surfaces of the nanotubes, so that short-circuiting at the time of contact is prevented. If this coating film is formed so that it is not limited to the nanotubes but extends to other wiring areas, then the insulating properties of the nanotweezers as a whole is enhanced. This insulating treatment is applicable to electrostatic type nanotweezers of any structure.
A second weak point of conventional devices is that the nanotweezers are weak and brittle in terms of strength, and this is because the nanotubes are fastened to a pointed glass tube. In order to alleviate this drawback, it is hereby proposed that the pyramid portion of an AFM (atomic force microscope) cantilever be used as a holder for the nanotubes. This pyramid portion is made of silicon or silicon nitride; as a result, the pyramid portion has electrical insulating properties and a much higher strength than conventional glass tubes.
The above-described two inventions will be comprehensively described here using a cantilever. The base end portions of two nanotubes are fastened to points near the apex of the pyramid portion, so that the tip end portions of these nanotubes are caused to protrude from the pyramid portion. Two types of nanotube fastening methods may be used. In the first method, areas near the base end portions of the nanotubes are irradiated with an electron beam inside an electron microscope. As a result of this irradiation, a carbon film or CVD film is formed as a coating film so that the base end portions of the nanotubes are covered. This coating film restrains the base end portions, and the nanotubes are firmly fastened. In the second method, the base end portions of the nanotubes are fused to the surface of the pyramid portion when these base end portions are directly irradiated with an electron beam. These fused portions fasten the nanotubes in place.
Next, lead wires are connected to the base end portions of the nanotubes. In the present invention, nanotubes or metal wiring formed by CVD (chemical vapor-phase deposition), etc. can be used as lead wires. For example, nanotubes are elements that have a high strength and an extremely high flexibility, and various diameters and lengths are available. Accordingly, such nanotubes are optimal as nano-size lead wires. Furthermore, metal atoms can be formed into very small wiring patterns by CVD.
One end of each nanotube lead wire is caused to contact the above-described base end portion of the corresponding nanotube, and this contact point is irradiated with an electron beam so that the nanotube lead wire is integrally fastened to the pyramid portion by spot welding. The other end of the nanotube lead wire may be connected to another nanotube lead wire or may be connected to an electrode film formed on the cantilever. Furthermore, CVD lead wires may be formed while being fastened to the base end portions of the nanotubes or to the surface of the pyramid portion.
After these lead wires are formed, a coating film consisting of an insulating material is formed on the base end portions of the nanotubes and over the entire area of each lead wire. Short-circuiting in an electrostatic system can be prevented by forming a coating film on the surfaces of the nanotubes. At the same time, the nanotweezers as a whole can be protected from short-circuiting, etc. by forming a coating film over the entire surface of the wiring. In such a case, there is no current leakage even if the nanotweezers are operated in electrolyte solutions such as biological fluids, etc. Electron beam irradiation or CVD may be utilized to form such a coating film.
Since the cantilever is relatively large, the connection of the electrode films on the cantilever with an external power supply circuit can be performed under an optical microscope or an optical magnifying glass. Such an external power supply circuit is constructed from a power supply, a voltage control circuit and an electrical switch. If the applied voltage is freely adjusted by means of the voltage control circuit, the degree of opening between the tip ends of the nanotubes can be arbitrarily adjusted, so that the opening and closing of the nanotweezers can be controlled in accordance with the size of the nano-substance that is being handled.
Furthermore, piezo-electric film type nanotweezers which are completely different from the electrostatic attraction type are also presented herein. In this piezo-electric film system, the nanotubes can be freely flexed by the expansion and contraction of a piezo-electric film, so that the tip ends of the nanotubes can be opened and closed. Accordingly, since no current flows between the nanotubes, the nanotweezers can be caused to function regardless of the electrical properties of the nano-substance.
In this piezo-electric film system, the holder of the nanotubes is not limited to an AFM or STM (tunnel microscope) holder. Probe needles used in a broad range of SPM (scanning probe microscopes) may be used. SPM probe needles are considerably larger than nanotubes in terms of size and have a sufficient size for the fastening of two nanotubes. The most effective holder is the pyramid portion of the AFM cantilever. This cantilever will be used in the following description.
First, the base end portions of two nanotubes are fastened to the pyramid portion of such a cantilever. In this case, the two nanotubes are placed so that the tip end portions of the nanotubes contact each other. In other words, the nanotubes are fastened so that the tip ends of the nanotubes are in contact. Fastening methods that can be used include the above-described coating film method and fusion method. Either of these fastening methods may be used.
Next, a piezo-electric film is formed on one of the two nanotubes. This piezo-electric film is also called a piezo-electric element and has the property of contracting when a voltage is applied. If the voltage is made variable, the amount of contraction also varies. When the piezo-electric film contracts, the nanotube to which this film is fastened flexes so that the nanotweezers open. Accordingly, the tip ends of the nanotubes are initially closed; and when a voltage is applied, the tip ends are opened, and the nano-substance is gripped in this open state. When the voltage is further increased, the degree of opening is increased, and the nano-substance is released. In cases where the nano-substance fails to separate from the nanotubes because of inter-molecular forces, the nano-substance can be electrically expelled by applying a voltage between the sample and the nanotubes.
One end of a nanotube lead wire may be connected to each end of the piezo-electric film, and the other ends of these nanotube lead wires may be connected to other nanotube lead wires. As described above, the lead wires may also be connected to electrode films on the cantilever. Indeed, CVD lead wires may also be utilized. Then, connections are made from these electrode films to an external power supply circuit. This external power supply circuit is comprised of a power supply, a voltage control circuit and an electrical switch. The operation of this circuit is done as described above.
Piezo-electric films may be formed on two nanotubes. In this case, two nanotubes can be flexed by the application of a voltage, so that the degree of opening of the tip ends of the nanotubes can be set at a larger value, thus making it possible to increase the performance of the nanotweezers.
A piezo-electric film is formed on the surface of the pyramid portion instead of being formed on the surfaces of the nanotubes. In this case, the pyramid portion is etched by means of a convergent ion beam device so that the pyramid portion is split into two pyramid pieces via the etched portion. The thickness of the respective pyramid pieces is adjusted so that the pyramid pieces possess flexibility. One nanotube is disposed on each pyramid piece so that the nanotube protrudes from the pyramid piece. Thus, a total of two nanotubes are provided so as to protrude in a manner that the tip ends of the nanotubes contact each other. A piezo-electric film is formed on the side surface of one or both pyramid pieces, and this piezo-electric film is caused to contract by applying a voltage to both ends of the piezo-electric film in the same manner as described above. As a result of this contraction, the pyramid piece(s) flex, and the tip ends of the nanotubes open. Afterward, the nanotubes function as nanotweezers by gripping or releasing nano-substances.
In the third invention, it is possible to use a construction, in either the electrostatic attraction system or piezo-electric film system, in which the nanotubes used in the nanotweezers consist of more than two nanotubes. For example, if three nanotubes are used, then nano-substances are gripped by these three nanotubes.
In a three-nanotube system, the three nanotubes are opened and closed. Instead, the opening and closing action of two of the three nanotubes may be controlled by an electrostatic attraction system. Furthermore, it is also possible to form piezo-electric films on two nanotubes so as to control the opening and closing action of the two nanotubes. In cases where the opening and closing of two of the three nanotubes is controlled, the remaining single nanotube functions as an auxiliary nanotube. In the three-nanotube system, since the nano-substance is gripped by three nanotubes, the gripping of nano-substances of various shapes such as spherical, rod-form, etc. can be accomplished more securely. In particular, if two nanotubes are set at the same polarity and one nanotube is set at a different polarity in the three-nanotube electrostatic system, the three nanotubes attract each other by an electrostatic attractive force. The gripping of nano-substances of unusual shapes becomes thus more secure.
In the piezo-electric film system as well, voltage application is accomplished by means of lead wires. Accordingly, by way of coating the surfaces of the piezo-electric films and the lead wires with an insulating substance, the danger of short-circuiting is eliminated. Consequently, the nanotweezers can also be operated in electrolyte solutions.
Not only conductive carbon nanotubes but also nanotubes in general such as insulating BCN nanotubes and BN nanotubes, etc. can be utilized as the nanotubes of the present invention. Carbon nanotubes are abbreviated as xe2x80x9cCNTxe2x80x9d and are manufactured utilizing the arc discharge of a carbon rod. In BCN nanotubes, some of the C atoms of CNT are replaced by B atoms and N atoms, and BN nanotubes are nanotubes in which almost all of the C atoms of CNT are replaced by B atoms and N atoms. Various methods have been developed as replacement methods. Conductive nanotubes include carbon nanotubes and insulating nanotubes which have a conductive film formed on the circumference of the nanotube.